avocado

A new avocado approach takes root

When the management of Amorentia Estate and Nursery near Tzaneen realised they had to replace their 35-year-old avocado trees, they confronted the reality that faces avocado growers across southern Africa. There is such a shortage of avocado plant material, that farmers have to wait many years for new trees.

In South Africa, nurseries supply new trees most of which are different cultivars grafted onto clonal rootstocks. As Amorentia manager, Wynand Espach explains, “we couldn’t wait six to seven years for trees, so we started looking at other options.”

About 90% of the estate’s avocado trees were initially planted on seedling rootstocks many years ago. After doing some research the Amorentia team found they could produce viable seedlings, not only for their own orchards, but for other interested growers. Howard Blight, the estate owner, had been invited to deliver a paper at the International Avocado Symposium in Lima, Peru in September 2015.

Howard traveled extensively through the avo producing highlands of Columbia and the coastal areas of Peru. He visited nurseries and saw successful plantings of avocadoes on seedling rootstocks.

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Seed that gets through the selection process is planted into germination beds.

DESERT-BORN CONCEPT

“While we were in Peru in 2015, we visited avocado orchards that Peruvians had established from seedlings. Now we have basically copied their methods and adapted it to local conditions,” says Howard.

These desert orchards on the western side of Peru get no rain. There is only about 2mm of fog precipitation from the ocean per year. The Peruvian government has drilled tunnels of up to 20km long through the Andes mountains, from which they siphon water from the Amazon river. From the western side of the mountains, water flows to the coast along canals.

Blocks of land of 20 000ha are available for farming in the areas to which the canals flow. The government sells the land to private enterprise at US$6 000 per irrigable hectare.

Peruvian avocado growers seized the opportunity and put up irrigation systems. They open trenches in the desert 1,5m wide and 1m deep which they fill with a mixture of compost and sand. The compost comes in by road.

Growers plant sterilised, germinated Columbian avocado seeds into bags. After two to three months the seedlings go through a selection process based on root configuration, the size of the trees and overall plant health. “Now you’ve got plants that are ready to plant into the field,” Wynand explains.

SEED FOR SOUTH AFRICA

To implement this system at home, Amorentia had to find a source of disease-free seed. For this they looked at a mountainous area in Mpumalanga, known for its large old avo trees dotting the rural landscape. “We went out there and found some spots with West Indian/Guatamalan cross trees, so we partnered with some of the locals to harvest seed and we started an avocado seedling nursery here at Amorentia,” Wynand says.

Having extensive experience in plant production and the 90,000 avo tree nursery they developed in Mozambique, Amorentia followed protocol with regards to tree identification, fruit picking, marking of individual trees, sunblotch virus testing, sanitising, seed selection, dipping and seed preparation.

‘In the nursery’s seed selection process, any seed with a mark is discarded.’

The trees identified as potential seed stock have been clearly marked and individually tested for viruses. Out of the 80 odd trees identified, not one tested positive for sunblotch virus.

“We picked between 30 and 50 fruits from each tree from various places and inspected them for size, shape, skin health etc,” says Wynand. “Fruit that was, for instance, too small automatically disqualified those trees.”

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Because the seedlings are planted directly into the field as soon as they are ready, Howard says it is not necessary to use 8kg bags as they do for trees on clonal rootstocks. The bags with the newly planted seedlings are placed on elevated, grooved, concrete slabs. The grooves drain water away and stop it from pooling, which encourages pathogen build-up.

Fruit that met the field selection criteria were brought back to Amorentia where the seed selection process started in earnest. Each box of seeds was marked corresponding to the tree number in Bushbuckridge. Large seeded fruit was selected.

“In the nursery’s seed selection process, any seed with a mark is discarded. We do not take any chances. We brought back 15 000 seeds on the first round of collections and we planted only 5 000, so we went through quite a strict selection process,” Wynand explains.

Once sterilised, the seeds that made the selection are planted in pre-germination beds covered in plastic for protection. Each tree’s number and the seed batch number is indicated on markers in the germination beds.

After germination there is another selection process. Anything with a less than perfect root system, or an odd shape is discarded. On the first round Amorentia threw away another five percent of the plant material at this stage.

Seeds are again sterilised, planted into 5kg bags and placed on concrete beds elevated above the soil. “We went the extra step of putting grooves into the concrete beds to make sure water runs off so that there is no standing water on the beds which reduces the risk of disease,” Howard explains.

The 5kg bags are big enough as these seedlings will soon be planted directly into the field where different cultivars will then be grafted onto them.

ANOTHER LESSON FROM PERU

Amorentia will also be taking a leaf out of the South Americans’ book for the grafting process. Because there’s no eco-system in the desert, the Peruvian farmers first plant rows of maize in very high density along with some grass to offer the avo seedlings shelter against the wind and some cover on the ground.

The seedlings, standing between 400mm and 500mm high are planted between the maize rows. The maize plants later become mulch and each tree gets a little plastic wind shelter.

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An avocado seedling. The waiting period for trees to establish new avo orchards can be dramatically reduced, using these seedlings, says Howard Blight of Amorentia nursery and Estate near Tzaneen.

When the new seedlings have a stem about as thick as a man’s thumb the farmers start grafting using a special technique where they make a small incision on the side of the seedling. They peel back the cambium and graft onto the seedling in the land. The graft is taped up so that the stem of the seedling serves as a stake for the new graft. “After six weeks your graft already shows flush, depending on the time of year,” says Howard.

In South America, Howard inspected orchards, individual trees and their root profiles at various growth stages and saw trees with even and continuous root systems of 1,2 m deep only 140 days after planting. The Peruvians use drip irrigation in the desert. “After two years they have the first flowers and within 36 months they were in production,” Howard explains. There is no time lost when growers use this method.

MUCH NEEDED ALTERNATIVE

“With clonal root stocks being the only option to South African farmers until now, there’s such a shortage of material here that we need to modify our thinking and approach if we don’t want to stifle the growth of the avocado industry,” says Howard. “We’re confident that quality seedlings as rootstock can go a long way in pushing through the bottleneck on the supply side of plant material.” South African orchards older than 20 years are on seedling rootstocks.

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These seedlings will soon be ready to transplant into orchards. Once the stems are thick enough the new cultivars will be grafted onto them.

Howard says countries like Chile, Peru and Mexico use seedlings successfully on a very large scale. “In Columbia they do both, clonal rootstocks and seedling rootstocks. Clonal rootstocks seem to have a growth advantage over seedlings for the first two years, but after three to four years the seedling rooted trees have caught up with the clonals and one would be hard-pressed to tell the difference. We experienced this in our avo orchard development in Mozambique.”

FROM THE NURSERY TO THE FIELD

Farmers who buy seedlings have a number of options when it comes to grafting on their own selected cultivars. Amorentia has trained its staff in the Peruvian grafting method and farmers can bring their workers for similar training. Amorentia staff will also go out to farms and train the farm workers to graft.

“Grafting material will come from various tested indexed trees. We’re not suggesting taking grafts from your fuerte or hass orchards grafting them without testing them,” Wynand explains.

Amorentia produces large numbers of carefully selected seedlings every year and is able to deliver on orders within 12 months.

For information contact Wynand Espach: wynand@amorentia.co.za

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